1. Field of the Invention
The present invention relates to a ceramic filter utilized in the production of food, drink, pharmaceuticals and so forth. It also relates to a process for manufacturing the same.
2. Description of The Related Art
In food industries or pharmaceutical industries, ultrafiltration or the like using ceramic filters has been hitherto carried out to remove unwanted substances included in stock solutions or to concentrate given substances in stock solutions.
Such ceramic filters gradually are plugged with their use because of organic matters such as proteins, resulting in a lowering of filtering performance. Accordingly, as a conventional means, ceramic filters are washed with an alkali or an acid to remove organic matters so that the filtering performance can be restored.
Since, however, ceramic filters contain not only Al.sub.2 O.sub.3 as a main component but also alkali- or acid-soluble components such as SiO.sub.2, CaO and Na.sub.2 O, and these components are dissolved out as a result of washing to bring about a great lowering of the performance.
To eliminate the above disadvantages, Japanese Laid-open Patent Application No. 59-225716 proposes to produce a filter using alumina with a high purity of 99.9% or more, and Japanese Laid-open Patent Application No. 63-197510 proposes to add MgO and ZrO.sub.2 as sintering aids.
Of the above methods, the method in which alumina with a high purity is used makes it necessary to carry out sintering at a high temperature and requires a special sintering furnace. In addition, alumina coarse particles of from 20 to 30 .mu.m in particle diameter must be sintered in order to obtain a filter of about 10 .mu.m in pore size. In such an instance, no sufficient strength can be obtained even if MgO and ZrO.sub.2 are added as sintering aids, unless the sintering is carried out at a high temperature of 1,800.degree. C. or more.